CHEM 2211 1st Edition Lecture 7 Outline of Last Lecture I IUPAC systematic naming Outline of Current Lecture I IR spectrums Current Lecture IR Spectrums What is IR spectrum It stands for infrared spectroscopy It is a type of graph we could say and we use it to identify compounds in organic chemistry The spectrum is obtained by passing infrared radiation through a compound sample This results in a plot of the percent transmitted of radiation versus the wavenumber radiation transmitted Bonds Bonds between atoms stretch and bend Stretching Is a vibration along the line of the bond It changes the bond length Bending Is a vibration along the does not occur along the line of the bond A bending vibration changes the bond angle Infrared radiation has the right range of frequencies to correspond to the stretching and bending of bonds These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute When a molecule is bombarded with infrared radiation at the right frequency for a bond it absorbs the radiation Depending on the wavenumber of the energy absorbed we can identify what kind of bond it is by using the spectrum An IR spectrum can be divided into two regions The functional group region The fingerprint region The functional group region Is where the functional groups are mostly absorbed This is the area from 4000 to 1400 cm 1 This is the area we focus on when using IR spectrums Even if a molecule had the same functional groups they would show up differently because they would be in different environments The fingerprint region Is specific to the molecule as a whole Is it the area from 1400 to 600 cm 1 We do not pay attention to this area at all Functional groups Functional groups show absorption bands at different ranges of wavelengths on the spectrum o Ketones o Esters o Amides o Alcohols Types of intensities The wavenumbers tell you where to look for a certain group or bond But you also need to know what intensity to look for There are three o Weak o Medium o Strong There can be a range to like o Medium weak o Medium strong When looking from the bottom of a spectrum to the top the closer the signal is to the bottom the stronger it is Ex red strong signal blue medium signal black weak signal Signals can also be broad or sharp the blue circled medium point is also sharp and the green circled point is a broad point
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